It is well known in the prior art that certain electrical signals can be used to synchronize a plurality of video and audio recording and editing machines. These electrical signals, commonly known as "Time Code" signals, enhance the value of these machines during the production and editing of audio and video recordings by providing a single reference signal for timing and control purposes.
These "Time Code" signals are standardized and fully described as "ANSI/SMPTE 12M-1986" which is incorporated herein by reference. The "Time Code" signals are commonly referred to as "Linear Time Code" or "SMPTE Time Code".
In use, SMPTE time code consists of eighty (80) bits of information describing timing references and other synchronization information. According to the ANSI standard, the timing code reference describes where along a recording space audio and video information may be found.
Time code describes the entire recording space in terms of hours, minutes, seconds and frames in order to assure that any audio and video information is perfectly synchronized according to human perception. Essentially, using eight decimal digits describing hours/minutes/seconds/frames, the time code can designate where in any twenty four hour period a sound or video signal should be properly placed within human perception.
The most particular designation within the time code reference describes an exact video frame along a series of frames defining an entire moving video image. The time code recognizes that there are exactly a certain number of video frames played in any single second and creates a time code address for every particular frame. In order to do this, the SMPTE standard recognizes that different countries and regions use a different number of frames per second and tries to account for this differing "frame rate" within the time code designation.
Generally, the frame rates which have come into standard practice in the audio and video recording industries, are precisely 30, 30/1.001, 25, and 24 frames per second (fps). In the Western world, these four frame rates correspond to monochrome (black and white) television (30 fps); color television and video (30/1.001 fps); film (24 fps); and European television (25 fps). A digital generator must precisely generate exact frame rate reference signals for each of these standards in order to be useable in multiple countries around the world.
Digital signal generators have typically utilized a series of divider circuits or adder circuits to generate a plurality of digital signals from a single master clock. However, such signal generators are limited in the number of frequencies that can be exactly generated and further suffer from complexity and high cost.
U.S. Pat. No. 4,108,035 to Alonso discloses an electronic music system that converts electrical signals into corresponding sound waves to create musical notes having desired timbres and musical characteristics. Alonso's musical generator uses a note oscillator in an electronic musical system to create synthetic music.
Alonso's note oscillator applies a modulo adder to generate carry pulses at a rate that is controlled by two numbers called an increment number and a divisor number. Using a keyboard, a musician selects notes to be played.
These notes are converted into digital signals and fed into a note calculator which selects the increment and divisor numbers to be used by the note oscillator. The note calculator selects the increment and divisor based upon a sound frequency determinative formula f.sub.n =CR (I/(1+B-D)), where f.sub.n is the frequency, CR is the clock rate, B is the modulus of an adder, I is the increment and D is the divisor.
Alonso's note oscillator is illustrated herein in FIG. 1. As shown in FIG. 1, the selected divisor 26 and increment 27 are input to initial storage circuitry consisting of the divisor number register 32 and the increment number register 34, respectively. The registers 32, 34 continuously feed the stored divisor 26 and increment 27 to multiplexer 40.
Depending upon the value of the gating signal 60, the multiplexer 40 feeds either the divisor 26 or the increment 27 to the modulo 8 adder 44. The adder 44 clocks through addition operations to add an addend AD, consisting of the multiplexed divisor 26 or increment 27, summed with an augend AU, consisting of an accumulated sum of previous additions stored in accumulator 52.
The adder 44 generates a sum S of the augend AU and addend AD. The adder 44 also generates a carry pulse CP when the sum S exceeds the modulo number of the adder 44. When the carry pulse CP is generated the sum S is the remainder of the addition operation and is determinative of the range of addition operations which must be covered before the next carry pulse CP is generated.
The carry pulse CP is thereby generated at the desired audio frequency and is fed through an output latch 58 to both a tone generator for synthesizing musical sound waves, and to the multiplexer 40 as gating signal 60 to multiplex the divisor 26 as the addend AD. When the carry pulse CP is not generated the increment 27 is multiplexed to the adder 44 by multiplexer 40 and the tone generator does not receive an input signal.
The operation of Alonso's oscillator is very complicated. Alonso requires that a note calculator chooses the frequency dependent Increment and Divisor. Alonso must then multiplex between the divisor number and the increment number every time a carry pulse occurs, and a number of attendant registers, memory devices and latches are required to keep track of the increment, divisor and accumulated sums. Furthermore, Alonso's note oscillator is even more complicated by the need to readjust the range of addition which is to be performed by the adder every time a tone generator input is to be produced in proportion to the remainder in response to each carry pulse. Lastly, Alonso's note oscillator is used solely to create an input to a tone generator in order to create synthetic musical tones and is not applied in any other manner.